This application is the National Stage of International Application No. PCT/GB99/02443, filed Jul. 26, 1999, which claims priority to UK Patent Application No. 9816675.4, filed Jul. 30, 1998.
The invention relates to a fluid motor, in particular a fluid motor of the type having a plurality of fluid actuated advancing elements such as pistons cooperating with a drive cam profile to achieve linear or rotational movement.
Various fluid motors are known in the art. For example known air motors include a rotor incorporating an eccentric or lobed cam having a plurality of pistons provided on a stator around it. The pistons are driven by air in sequence such that the lobed cam is advanced by the pistons to give rise to rotation of the rotor.
GB 2109056 relates to a fluid motor in which a tri-lobed cam is mounted on a rotor with four pistons disposed symmetrically around it to drive it. The pistons also act as valves governing the supply and exhaust of drive fluid to other of the pistons.
A problem associated with known fluid motors is that variations in the output torque are unacceptably high.
According to the present invention there is provided a fluid motor comprising a stator part and an advancable part advancable relative to the stator part, in which one of said parts includes a drive cam profile and the other part includes one or more fluid actuated advancing elements arranged to traverse the drive cam profile to advance the advancable part relative to the stator part, in which the drive cam profile is substantially sinusoidal. As a result substantially constant torque is achievable.
Preferably a plurality of advancing elements are provided each arranged to advance the advancing part during an advancing stroke, at least some of the advancing strokes overlapping temporally. Preferably the full stroke of an advancing element is 360xc2x0 of the full stroke, the advancing stroke comprising 180xc2x0 of the full stroke and sequential advancing strokes of respective advancing elements overlap by 90xc2x0. Preferably the parts are rotationally advancable relative to one another and the drive cam profile comprises a linear substantially sinusoidal profile mapped onto a circular geometry. Preferably the advancing elements are mounted to oscillate on the stator part and the advancable part comprises a rotor part. Preferably the advancing elements are provided in synchronised opposing pairs on the stator part allowing radial or axial forces to be balanced.
Preferably the drive cam profile on the rotor part is disposed radially outside the stator part and the advancing elements oscillate in a radial direction; alternatively the drive cam profile on the rotor part may be disposed radially inside the stator part and advancing elements may oscillate in a radial direction; alternatively the drive cam profile on the rotor part may be disposed axially outside the stator part and the advancing elements may oscillate in an axial direction.
Alternatively the parts may be linearly advancable relative to one another and the advancing elements may oscillate in a direction transverse to the linear advancing direction.
Preferably the advancing elements comprise reciprocating pistons and either the number of pistons is a multiple of four and the number of lobes on the drive cam profile is a multiple of three or the number of pistons is a multiple of six and the number of lobes on the drive cam profile is a multiple of eight to achieve optimum torque from the pistons.
At least one actuable valve is preferably provided to control fluid actuation of the or each advancing element, a valve cam profile preferably being provided fixed relative to the drive cam profile, and the valve cam profile preferably cooperating with the valve to control actuation of the valve.
Alternatively at least one actuable valve is preferably provided to control fluid actuation of the or each advancing element, electronic control means being provided to control actuation of the valve.
Preferably the stator part and advancing part are symmetrically arranged allowing the motor to be stalled and/or operated in reverse. The advancing elements may comprise double acting pistons.
According to the invention there is further provided a fluid motor comprising a stator part and an advancable part advancable relative to the stator part, in which one of said parts includes a drive cam profile and the other part includes one or more fluid actuated advancing elements arranged to traverse the drive cam profile to advance the advancable part relative to the stator part, in which one or more valves is provided to control fluid actuation of the or each drive element, in which a valve cam profile is provided fixed relative to the drive cam profile, and in which the valve cam profile cooperates with the or each valve to control actuation of the valve. As a result direct synchronisation can be achieved without affecting the performance of the pistons directly.
The valve may include a cam follower valve actuation controller mechanically linked to the valve and arranged to follow the valve cam profile to control actuation of the valve; alternatively a valve cam profile follower may be arranged to generate a control signal representative of its position on the valve cam profile and the valve may be electronically actuated dependent on the control signal.
According to another aspect of the invention there is provided a fluid motor comprising a stator and a rotor in which the rotor includes a drive cam profile and the stator includes a fluid actuated advancing element arranged to oscillate in a radial direction to traverse the cam profile to advance the rotor relative to the stator, in which the drive cam profile on the rotor is disposed radially outside the stator. As a result the torque output is smoothed as the individual advancing element strokes each contribute only a small advancement of the rotor.
Preferably there is a rotor shaft around which the stator is provided, a drive cam profile support extending from the shaft and a valve cam profile provided on the drive cam profile support spaced from the drive cam profile in which at least one actuable valve is provided to control fluid actuation of the or each drive element and in which the valve cam profile cooperates with the valve to control actuation of the valve.
According to another aspect there is provided a fluid motor comprising a stator and a rotor, in which the rotor includes a drive cam profile and the stator includes a fluid actuated advancing element arranged to oscillate in the axial direction to traverse the drive cam profile to advance the rotor relative to the stator in which the drive cam profile is disposed axially outside the stator and includes first and second parts disposed axially outside opposing sides of the stator. As a result both axial and radial symmetry is achieved, allowing the forces to be balanced.
According to another aspect of the invention there is provided a fluid motor comprising a stator part and an advancable part advancable relative to the stator, in which one of said parts includes a drive cam profile and the other part includes a fluid actuated advancing element arranged to traverse the drive cam profile and advance the advancable part relative to the stator part, in which the parts are linearly drivable relative to one another.
According to another aspect there is provided a fluid motor comprising a stator part and an advancable part drivable relative to the stator part in which one of said parts includes a drive cam profile and the other part includes one or more fluid actuated advancing elements arranged to traverse the drive cam profile to advance the advancable part relative to the stator part, in which one or more valves is provided to control fluid actuation of the or each advancing element and actuation of the valve is controlled dependent on the relative position of the two parts.
The invention also comprises a valve actuator including a fluid motor of the type discussed herein.